The blade holder is subjected at the two ends which are located outside the screen to the action of the above-mentioned forces of application of the doctor blade against the screen whilst the remainder of its length is subjected by means of the doctor blade to the reaction of the screen which bears on the material being printed. However, by reason of the fact that the blade holder is housed within the interior of the cylindrical screen, it has a substantial length with respect to its cross-section. In consequence, the blade holder is subjected to a certain bending stress which makes it concave in a downward direction; thus the doctor blade which is usually fixed along the bottom portion of said blade holder has a corresponding concavity and there is an attendant disadvantage in the resultant lack of uniformity of pressure applied to the screen by the different points along the length of the doctor blade. This in turn results in defective operation, especially in faulty distribution of the color which flows through the screen along the generator-line of contact between the screen and the material to be printed.